[DeTomaso] Piston Ring Rotation.

Asa Jay Laughton asajay at asajay.com
Sat May 26 22:27:14 EDT 2012


I've created an illustration of the piston compression ring gaps on the 
disassembly of my old Mach I engine.

http://www.teampanteraracing.com/index.php?option=com_g2bridge&view=gallery&Itemid=57&g2_itemId=4970

In that same gallery I've posted a few photos of the main bearings and 
other wear.

Asa Jay

Asa Jay Laughton, MSgt, USAFR, Retired
&  Shelley Marie
Spokane, WA
******************************
http://www.racingagainstautism.com
http://www.teampanteraracing.com
http://facebook.com/racingagainstautism


On 5/26/2012 11:58 AM, Asa Jay Laughton wrote:
> Most of us are aware of the proper ring positioning when assembly an engine:
> http://www.351c.info/gallery2/d/218-1/ringspacing.jpg
> The two compression rings should be spaced about 30* (or about one inch)
> from the front centerline of the piston, one on either side.  The oil
> ring segments are the same on the opposite  side of the piston toward
> the rear.  The illustration above shows this quite well.
>
> But do the rings rotate after assembly?
>
> A few years ago at the POCA Fun Rally, Jack had an expert who was
> familiar with pistons.  He said indeed the rings do rotate, so in the
> end it doesn't really matter where you index them to start with...
> they're going to move.
>
> Today I recorded the ring locations on my forensics engine.  I had been
> careful not to turn the rings on the pistons when I removed the
> pistons/rods from the engine previously.  Because I can't insure they
> didn't move at all, the relationships below are rounded.  Here are the
> results.  My "timing" is from the -front- of the engine, moving
> clockwise.  The piston position at 12 o'clock is the part facing front,
> the position at 6 o-clock is at the rear.
>
> The first compression ring is at the top, the second on the bottom.
>
> Piston    1st Comp    2nd Comp    Oil/Oil
> #1        8 o-clock   4 o-clock     4/2
> #2        10          11           12/3
> #3        10          2            10/1  (probably the only one closest
> to installed)
> #4        8           8             8/8  (All ring gaps were lined up)
>
> #5        9           2             5/5
> #6        12          9             5/5
> #7        5           4             6/5
> #8        9           3             3/7
>
> As you can see, they are all over the place.  I'll work up a good
> illustration and post it later.
>
> Does this mean I won't index them the next time I assemble and engine?
> Actually, I'll most likely still index them when assembling, only
> because I'm anal about those things and I do believe spacing them does
> assist with initial break in.  If they are spaced the same, I look at
> that as an easy path for compression gasses to get past.  In other
> words, gases might get past the lower tension oil ring segments and past
> the gap in the bottom compression ring but then they'll have to travel
> around the edge a while before they meet up with the gap in the upper
> ring.  In the end, it may not really matter.
>
> Asa Jay
> Pantera Research Institute, Pacific Northwest
>



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